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CRI and LED

Perth, 23rd February 2010

We are of course well familiar with the color rendering index (CRI) for traditional white light sources like halogen, metal halide or fluorescent. But when it comes to the CRI for white LED’s we are still much in unchartered waters it seems. Note there is a difference between white created by RGB LED and the so called phosphor coated white LED’s

As we are studying the white LED’s for application in our projects Iam trying to understand what actually is the “state of the art” in regards to white LED’s. It is obvious that all the rosy talk about life time, performance and colour characteristics were a bit over-optimistic to say the least. Now most manufacturers are in damage control and start to issue more “reliable” information about the LED performances. From the manufacturers information I find that from the commercially available white LEDs the CRI is somewhere between 70 and 90. Contrary to RGB LED’s creating white with a CRI of only between 25 to 70 or thereabouts.

Though dated 2007, a report prepared by the CIE’s technical committee investigating the color rendering of white LED light sources, concluded, and I quote: “the CRI is generally not applicable to predict the colour rendering rank order of a set of light sources when white LED light sources are involved in this set.” The academic studies and visual appraisal experiments with observers showed there was a poor correlation between the rankings by observation and the calculated values.

I understand that the CIE and probably other lighting researchers are investigating this issue with the aim to come up with a new system to replace eventually the current CRI. While still useful for traditional light sources it is obvious we should be mindful when using the CRI for white LED light sources.